Chronic obstructive pulmonary disease is a persistent obstruction of the airways caused by chronic bronchitis and pulmonary emphysema. In the United States alone, approximately fourteen million people suffer from some form of chronic obstructive pulmonary disease and it is in the top ten leading causes of death.
Air enters the mammalian body through the nostrils and flows into the nasal cavities. As the air passes through the nostrils and nasal cavities, it is filtered, moistened and raised or lowered to approximately body temperature. The back of the nasal cavities is continuous with the pharynx (throat region); therefore, air may reach the pharynx from the nasal cavities or from the mouth. Accordingly, if equipped, the mammal may breathe through its nose or mouth. Generally air from the mouth is not as filtered or temperature regulated as air from the nostrils. The air in the pharynx flows from an opening in the floor of the pharynx and into the larynx (voice box). The epiglottis automatically closes off the larynx during swallowing so that solids and/or liquids enter the esophagus rather than the lower air passageways or airways. From the larynx, the air passes into the trachea, which divides into two branches, referred to as the bronchi. The bronchi are connected to the lungs.
The lungs are large, paired, spongy, elastic organs, which are positioned in the thoracic cavity. The lungs are in contact with the walls of the thoracic cavity. In humans, the right lung comprises three lobes and the left lung comprises two lobes. Lungs are paired in all mammals, but the number of lobes or sections of lungs varies from mammal to mammal. Healthy lungs, as discussed below, have a tremendous surface area for gas/air exchange. Both the left and right lung is covered with a pleural membrane. Essentially, the pleural membrane around each lung forms a continuous sac that encloses the lung. A pleural membrane also forms a lining for the thoracic cavity. The space between the pleural membrane forming the lining of the thoracic cavity and the pleural membranes enclosing the lungs is referred to as the pleural cavity. The pleural cavity comprises a film of fluid that serves as a lubricant between the lungs and the chest wall.
In the lungs, the bronchi branch into a multiplicity of smaller vessels referred to as bronchioles. Typically, there are more than one million bronchioles in each lung. Each bronchiole ends in a cluster of extremely small air sacs referred to as alveoli. An extremely thin, single layer of epithelial cells lining each alveolus wall and an extremely thin, single layer of epithelial cells lining the capillary walls separate the air/gas in the alveolus from the blood. Oxygen molecules in higher concentration pass by simple diffusion through the two thin layers from the alveoli into the blood in the pulmonary capillaries. Simultaneously, carbon dioxide molecules in higher concentration pass by simple diffusion through the two thin layers from the blood in the pulmonary capillaries into the alveoli.
Breathing is a mechanical process involving inspiration and expiration. The thoracic cavity is normally a closed system and air cannot enter or leave the lungs except through the trachea. If the chest wall is somehow compromised and air/gas enters the pleural cavity, the lungs will typically collapse. When the volume of the thoracic cavity is increased by the contraction of the diaphragm, the volume of the lungs is also increased. As the volume of the lungs increase, the pressure of the air in the lungs falls slightly below the pressure of the air external to the body (ambient air pressure). Accordingly, as a result of this slight pressure differential, external or ambient air flows through the respiratory passageways described above and fills the lungs until the pressure equalizes. This process is inspiration. When the diaphragm is relaxed, the volume of the thoracic cavity decreases, which in turn decreases the volume of the lungs. As the volume of the lungs decrease, the pressure of the air in the lungs rises slightly above the pressure of the air external to the body. Accordingly, as a result of this slight pressure differential, the air in the alveoli is expelled through the respiratory passageways until the pressure equalizes. This process is expiration.
Chronic obstructive pulmonary disease is a persistent obstruction of the airways caused by chronic bronchitis and pulmonary emphysema. Chronic bronchitis and acute bronchitis share certain similar characteristics; however, they are distinct diseases. Both chronic and acute bronchitis involve inflammation and constriction of the bronchial tubes and the bronchioles; however, acute bronchitis is generally associated with a viral and/or bacterial infection and its duration is typically much shorter than chronic bronchitis.
In chronic bronchitis, the bronchial tubes secrete too much mucus as part of the body's defensive mechanisms to inhaled foreign substances. Mucus membranes comprising ciliated cells (hair like structures) line the trachea and bronchi. The ciliated cells or cilia continuously push or sweep the mucus secreted from the mucus membranes in a direction away from the lungs and into the pharynx, where it is periodically swallowed. This sweeping action of the cilia functions to keep foreign matter from reaching the lungs. Foreign matter that is not filtered by the nose and larynx, as described above, becomes trapped in the mucus and is propelled by the cilia into the pharynx. When too much mucus is secreted, the ciliated cells may become damaged, leading to a decrease in the efficiency of the cilia to sweep the bronchial tubes and trachea of the mucus containing the foreign matter. This in turn causes the bronchioles to become constricted and inflamed and the individual becomes short of breath. In addition, the individual will develop a chronic cough as a means of attempting to clear the airways of excess mucus.
Individuals who suffer from chronic bronchitis may develop pulmonary emphysema. Pulmonary emphysema may be caused by a number of factors, including chronic bronchitis, long term exposure to inhaled irritants, e.g. air pollution, which damage the cilia, enzyme deficiencies and other pathological conditions. Pulmonary emphysema is a disease in which the alveoli walls, which are normally fairly rigid structures, are destroyed. The destruction of the alveoli walls is irreversible. In pulmonary emphysema, the alveoli of the lungs lose their elasticity, and eventually the walls between adjacent alveoli are destroyed. Accordingly, as more and more alveoli walls are lost, the air exchange (oxygen and carbon dioxide) surface area of the lungs is reduced until air exchange becomes seriously impaired.
Mucus hyper-secretion and dynamic airway compression are mechanisms of airflow limitation in chronic obstructive pulmonary disease. Mucus hyper-secretion is described above with respect to bronchitis. Dynamic airway compression results from the loss of tethering forces exerted on the airway due to the reduction in lung tissue elasticity. In other words, the breakdown of lung tissue leads to the reduced ability of the lungs to recoil and the loss of radial support of the airways. Consequently, the loss of elastic recoil of the lung tissue contributes to the inability of individuals to exhale completely. The loss of radial support of the airways also allows a collapsing phenomenon to occur during the expiratory phase of breathing. This collapsing phenomenon also intensifies the inability for individuals to exhale completely. As the inability to exhale completely increases, residual volume in the lungs also increases. This then causes the lung to establish in a hyperinflated state. The individual develops dyspnea in which the individual can only take short shallow breaths. Essentially, air is not effectively expelled and stale air accumulates in the lungs. Once the stale air accumulates in the lungs, the individual is deprived of oxygen.
Another aspect of an emphysematous lung is that the communicating flow of air between neighboring air sacs is much more prevalent as compared to healthy lungs. This phenomenon is known as collateral ventilation. However, since air cannot be expelled from the native airways due to the loss of tissue elastic recoil and radial support of the airways (dynamic collapse during exhalation), the increase in collateral ventilation does not significantly assist an individual in breathing.
There is no cure for pulmonary emphysema, only various treatments, including exercise, drug therapy, such as bronchodilating agents, lung volume reduction surgery and long term oxygen therapy. Long term oxygen therapy is widely accepted as the standard treatment for hypoxia caused by chronic obstructive pulmonary disease. Typically, oxygen therapy is prescribed using a nasal cannula. There are disadvantages associated with using the nasal cannula. Transtracheal oxygen therapy has become a viable alternative to long term oxygen therapy. Transtracheal oxygen therapy delivers oxygen directly to the lungs using a catheter that is placed through and down the trachea. Bronchodilating drugs only work on a percentage of patients with chronic obstructive pulmonary disease and generally only provide short-term relief. Oxygen therapy is impractical for the reasons described above, and lung volume reduction surgery is an extremely traumatic procedure that involves removing part of the lung. The long term benefits of lung volume reduction surgery are not fully known.
Accordingly, there exists a need for safely and effectively accessing the lung or lungs for the treatment of various conditions.